1. Field of the Invention
The present invention relates to a bicycle fork, or to any other like article comprising two arms connected to a common body, based on a laminated material constituted by a resin reinforced by a textile reinforcement; it also relates to a process for obtaining such a fork.
2. Description of the Prior Art
In French Patent Application No. 83 08864 (publication No. 2 546 473), Applicant described a novel type of bicycle frame based on a tubular material constituted by a resin reinforced by a textile reinforcement, formed by a superposition of braided sheaths. The different tubular elements of cylindrical or conical section are assembled together by means of sleeves.
Taking into account the advantages offered by such a material and in order to obtain a homogeneous bicycle, it might have been envisaged to produce the fork in a similar way. However, production of this element, which is essentially composed of two sectioned blades (or sleeves) at the ends of which the wheel is fixed, a head connecting the two blades and a cylindrical pivot extending the head and on which the handlebar is fixed, by applying the teachings of the above Patent, does not give satisfaction in view of the delicate technical problems to be overcome, such as for example:
the difficulty in having a perfect symmetry between the two sleeves (or blades) of the fork;
the presence of a zone of weakness at the joint between the sleeves and the head, whilst it is this zone which is subjected to the highest mechanical stresses.
In order to overcome these drawbacks, it might have been envisaged to connect the sleeves and the head by overmoulding or by adhesion. However, tests made along these lines showed that, even by selecting resins known for their excellent mechanical strength, such as for example compounds based on polyester or epoxy resins reinforced with glass fibers, it was not possible to obtain a satisfactory fork, in view of:
a lack of homogeneity at the joint, resulting from a poor distribution of the cut fibers in the structure of the workpiece;
considerable creeping due to the mechanical stresses;
very low fatigue strength of the workpieces;
necessity of overdimensioning in order to compensate a very low modulus of elasticity.